Data from: The impact of hotspot-targeted interventions on malaria transmission in Rachuonyo south district in the western Kenyan highlands: a cluster-randomized controlled trial

BACKGROUND: Malaria transmission is highly heterogeneous, generating malaria hotspots that can fuel malaria transmission across a wider area. Targeting hotspots may represent an efficacious strategy for reducing malaria transmission. We determined the impact of interventions targeted to serologically defined malaria hotspots on malaria transmission both inside hotspots and in surrounding communities. METHODS & FINDINGS: Twenty-seven serologically defined malaria hotspots were detected in a survey conducted in June 2011 that included 17,503 individuals from 3,213 compounds in a 100 km2 area in Rachuonyo South district, Kenya. In a cluster-randomized trial in March 2012, we randomly allocated 5 clusters to hotspot-targeted interventions with larviciding, distribution of long-lasting insecticide-treated nets, indoor residual spraying and focal mass drug administration (2082 individuals in 432 compounds); 5 control clusters received malaria control following Kenyan national policy (2468 individuals in 512 compounds). Our primary outcome measure was parasite prevalence in evaluation zones up to 500 m outside hotspots, determined by nPCR at baseline and 8 (June 2012) and 16 weeks post-intervention (August 2012) by technicians blinded to the intervention arm. Secondary outcome measures were: parasite prevalence inside hotpots, parasite prevalence in the evaluation zone as function of distance to the hotspot boundary, Anopheles mosquito density, mosquito breeding site productivity, malaria incidence by passive case detection and the safety and acceptability of interventions. Intervention coverage exceeded 87 % for all interventions. Hotspot-targeted interventions did not result in a change in nPCR parasite prevalence outside hotspot boundaries (p?0.187). We observed an average reduction in nPCR parasite prevalence of 10*2% (95% CI -1*3 - 21*7%) inside hotspots 8 weeks post-intervention that was statistically significant after adjustment for covariates (p=0*024), but not after 16 weeks (p=0.265). We observed no statistically significant trend in the effect of the intervention on nPCR parasite prevalence in the evaluation zone in relation to distance to the hotspot boundary 8 weeks (p=0.27) or 16 weeks post intervention (p=0.75). Thirty-six patients with RDT-confirmed clinical malaria could be located to intervention or control clusters with no apparent difference between the study arms. In intervention clusters we caught an average of 1.14 female anophelines inside hotspots and 0.47 in evaluation zones; in control clusters we caught an average of 0.90 female anophelines inside hotspots and 0.50 in evaluation zones, with no apparent difference between study arms. Our trial was not powered to detect subtle effects of hotspot-targeted interventions nor designed for effects of interventions over multiple transmission seasons. CONCLUSION: Despite high coverage, the impact of interventions targeting malaria vectors and human infections on nPCR parasite prevalence was modest, transient and restricted to the targeted hotspot areas. Our findings suggest that transmission may not primarily occur from hotspots to the surrounding areas and that areas with highly heterogeneous but widespread malaria transmission may currently benefit most from an untargeted community-wide approach. Hotspot-targeted approaches may have more validity in settings where human settlement is more nuclear. TRIAL REGISTRATION: www.ClinicalTrials.gov NCT01575613